https://gitlab.torproject.org/tpo/core/tor/-/merge_requests/990

From 64b5638bf0d31e70f0832317fffc47c92b28e5ab Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Thu, 12 Feb 2026 14:56:58 -0500
Subject: [PATCH] Fix an absolutely silly pile-up of big-endian bugs in
 polyval.c

Only big-endian systems are affected.

First off, the non-gcc fallback algorithm for byte swapping was wrong:
We were OR-ing all the input bytes into the low 8 bits of the output.

Secondly, the non-gcc fallback code was broken: it was referring to "value",
when the input was called "v".

Finally and more significantly, the big-endian detection was wrong:
We were looking at WORDS_BIG_ENDIAN, when the actual autoconf macro
is WORDS_BIGENDIAN.

Closes bug #41215.
---
 changes/bug41215          |  3 +++
 src/ext/polyval/polyval.c | 31 ++++++++++++++++---------------
 2 files changed, 19 insertions(+), 15 deletions(-)
 create mode 100644 changes/bug41215

diff --git a/changes/bug41215 b/changes/bug41215
new file mode 100644
index 0000000000..d2d715ba5a
--- /dev/null
+++ b/changes/bug41215
@@ -0,0 +1,3 @@
+  o Minor bugfixes (portability):
+    - (Hopefully) fix our polyval implementation on big-endian platforms.
+      Fixes bug 41215; bugfix on 0.4.9.3-alpha.
diff --git a/src/ext/polyval/polyval.c b/src/ext/polyval/polyval.c
index 9f64734e0f..157ba54044 100644
--- a/src/ext/polyval/polyval.c
+++ b/src/ext/polyval/polyval.c
@@ -84,38 +84,39 @@ static void pv_mul_y_h(polyval_t *);h
 /* =====
  * Endianness conversion for big-endian platforms
  */
-#ifdef WORDS_BIG_ENDIAN
+#ifdef WORDS_BIGENDIAN
 #ifdef __GNUC__
 #define bswap64(x) __builtin_bswap64(x)
 #define bswap32(x) __builtin_bswap32(x)
 #else
 /* The (compiler should optimize these into a decent bswap instruction) */
 static inline uint64_t
-bswap64(uint64_t v)
+bswap64(uint64_t value)
 {
   return
     ((value & 0xFF00000000000000) >> 56) |
-    ((value & 0x00FF000000000000) >> 48) |
-    ((value & 0x0000FF0000000000) >> 40) |
-    ((value & 0x000000FF00000000) >> 32) |
-    ((value & 0x00000000FF000000) >> 24) |
-    ((value & 0x0000000000FF0000) >> 16) |
-    ((value & 0x000000000000FF00) >> 8) |
-    ((value & 0x00000000000000FF));
+    ((value & 0x00FF000000000000) >> 40) |
+    ((value & 0x0000FF0000000000) >> 24) |
+    ((value & 0x000000FF00000000) >> 8) |
+    ((value & 0x00000000FF000000) << 8) |
+    ((value & 0x0000000000FF0000) << 24) |
+    ((value & 0x000000000000FF00) << 40) |
+    ((value & 0x00000000000000FF) << 56);
 }
-static inline uint64_t
-bswap32(uint64_t v)
+
+static inline uint32_t
+bswap32(uint32_t value)
 {
   return
     ((value & 0xFF000000) >> 24) |
-    ((value & 0x00FF0000) >> 16) |
-    ((value & 0x0000FF00) >> 8) |
-    ((value & 0x000000FF));
+    ((value & 0x00FF0000) >> 8) |
+    ((value & 0x0000FF00) << 8) |
+    ((value & 0x000000FF) << 24);
 }
 #endif
 #endif
 
-#ifdef WORDS_BIG_ENDIAN
+#ifdef WORDS_BIGENDIAN
 #define convert_byte_order64(x) bswap64(x)
 #define convert_byte_order32(x) bswap32(x)
 #else
-- 
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